1. Field of the Invention
The present invention relates to an image reading apparatus configured to optically read an original.
2. Description of the Related Art
In the related art, an image reading apparatus configured to convey and read an original is used to perform image reading of the original. Specifically, a motor is driven to move and stop a reader portion nearly directly under a reading position. Then, light is irradiated from a lamp unit, and the originals stacked on the original tray are separated one by one and are conveyed along a glass member that supports the original in the reading position. In addition, the original is optically scanned over the glass member, and reflection light thereof is read by the reader portion, so as to obtain image data. Meanwhile, there is known a technique of reading both sides of the original by arranging reader portions in both sides of an original conveyance path and conveying the original once without reversing the original (Japanese Patent Laid-Open No. 2008-199213).
In such an image reading apparatus, it is necessary to perform shading correction on a regular basis by correcting unevenness of a density level generated by a characteristic of an image pickup element, an influence of lens aberration, and the like in order to constantly maintain an image reading precision.
In an image reading apparatus in the related art, in order to perform shading correction of the reader portion, a glass member to which a white reference member is attached moves such that the reader portion faces the white reference member, and the white reference is read.
In the apparatus that optically reads an image as described above, if the original supported by the glass member in the image reading position is uplifted or rattled, it is difficult to perform reading with a high precision. For this reason, a guide portion or a subsidiary conveyance roller that presses the original to the glass member in the image reading position is provided. However, it is necessary to position such an element with respect to the glass member with a high positional precision. In this regard, the positioning is performed by causing the guide member and the like to abut on the glass member.
However, if the guide member or the like abuts on the glass member, the guide member and the glass member may rub together and wear out when the glass member moves in a case where shading correction is performed as described above. As a result, the positional precision may be degraded.